Automobile mats used for covering the flooring of an automobile are typically molded, laminated products composed of a tufted carpet having a padding of thermoplastic material laminated to the back surface. Either prior to or after the carpet has been molded to conform to the interior of the automobile, plastic or rubberized components are bonded to the carpet to form the "heel pads" and other wear portions of the floor mats, transmission tunnel and areas of the carpet which undergo the most wear during use.
In the past, a number of conventional methods for laminating a PVC heel pad to the carpet have been used on a commercial basis, and many prior art methods have attempted to achieve three principal objectives--first, to provide a secure and uniform bond between the carpet or floor mat and the entire surface area of the heel pad in contact with the carpet, including the edges; second, to affix the heel pad in such a manner that the edges remain trimmed and aesthetically appealing following adhesion to the carpet; and third, to provide a heel pad having sufficient abrasion and scuff resistance to ensure that the pad will last at least as long as the carpet itself.
One well known process for applying heel pads to automobile carpets is the so-called "dielectric" method which permanently bonds polyvinyl chloride pads to the carpet while simultaneously forming the design pattern. The dielectric process uses short wave radio waves (microwaves) to increase the molecular activity of a PVC blank in a conventional pattern mold such that the collision frequency between molecules causes an increase in the heat of friction, which in turn causes the PVC to plasticize and adhere to the carpet fibers while forming a design pattern on the opposite surface. One advantage of the dielectric process is that it accomplishes the required adhesion without substantially increasing the heat o the metal pattern mold used to apply the PVC heel pad and form the desired pattern.
The dielectric process does not require the use of any adhesive composition, hot melt or otherwise, and has proven to be a commercially viable laminating technique. However, the process has a number of distinct disadvantages. First, because of the relatively complex and expensive equipment required, such processes have extremely high maintenance costs (requiring, in applicant's case, over $30,000 dollars a year in routine plant maintenance and repairs). Generally, the entire dielectric operation must be shut down for both periodic and routine scheduled repairs, resulting in 2 to 3 days down-time for the equipment involved. The dielectric process is also high in operating costs because it consumes electrical energy at a relatively high rate.
Preferably, the dielectric process is carried out on a flat carpet (although it has been employed with pre-molded carpets). In such applications, a separate molding operation is required which may involve a series of additional processing steps. For example, a flat carpet which already has the heel pad affixed to one portion will invariably require reheating before the carpet can be molded for installation in the automobile. During such subsequent molding operations, the carpet backing (generally consisting of a thermoplastic material) plasticizes causing the position of the molded carpet to shift relative to the backing as much as 1/2 inch. This tendency to "drift" during the subsequent heating and molding process can result in a variance in the position of the previously-applied heel pad on the molded carpet and thereby cause quality assurance problems in the final end product.
A further disadvantage of conventional dielectric processes concerns the arcing which may result from the use of radio wave heating elements. For example, virtually any amount of metal present in either the carpet or the heel pad will tend to arc during the dielectric heating process and burn the heel pad thereby ruining the carpet. Even pigments, dyes and plasticizers with traces of metal or metallic salts in the carpet may cause arcing and result in unscheduled repair and maintenance costs. Also, any residual traces of premetallized acid dyes (normally used in the manufacture of automotive carpeting) to achieve good fastness to ultra-violet light may cause such arcing. Again, the above problems may result in quality control problems with the end-product molded carpet.
A known alternative to the dielectric process is the use of hot melt adhesives, commonly referred to as "thermoplastic resins" or "thermoplastic adhesives" to affix backings and reinforcements to the automotive carpet. Hot melt adhesives are well known for their ability to form a rapid bond during the lamination of, for example, padding or a thermoplastic material to the back surface of the carpet.
Heretofore it has also been known that hot melt adhesives, including polyamides and polyester resins, could be used to apply polyvinyl chloride heel pads to carpeting. However, conventional processes using such adhesives require preformed, prepatterned PVC heel pads having thicknesses measuring about 40 millimeters. Such adhesives have not been used for purposes of adhesively bonding an unpatterned blank pad to the carpet and simultaneously forming a design pattern on the exterior surface of the pad.
One known conventional process for applying a PVC heel pad to carpeting utilizes an adhesive compound applied to only portions of the PVC pad (e.g., the edges or other areas, depending on the automobile manufacturer's requirements) using a relatively thick prepatterned pad, i.e., a pad which has a design pattern already embossed on the exterior surface. A number of problems exist with such a lamination technique, including higher cost due to the pre-molding operation for the pad to form the desired pattern, the lack of adhesion due to the fact that a uniform layer of adhesive is not applied to the entire pad (thereby making the bond between the pad and carpet non-uniform in certain areas), and the difficulties encountered in ensuring that the adhesive applied to the pad does not flow under the edges of the pad and into the carpet or does not flow completely to the edge, thereby leaving a portion of the edge unglued.
A third known method for applying a heel pad to tufted carpet requires that the pad be pre-formed and thereafter sewn directly to the carpet, with or without adhesive bonding to one or more portions of the pad. The disadvantages of such method are the time and cost to prepattern the pads, the cost to perform the subsequent sewing and bonding operations, the non-uniformity of the carpet/pad bond and the generally shorter wear life expectancy for sewn, as opposed to fully laminated articles.
Within the automotive industry, all of the above prior art methods have typically used polyvinyl chloride unpatterned blanks or prepatterned PVC pads having thicknesses in the range of 30-50 millimeters, depending on the desired application and the automobile manufacturer's standard for interior carpeting. These conventional heel pad thicknesses have been necessary for two reasons. First, a minimum pad thickness is essential to allow for acceptable thermal flow design pattern formation during the dielectric process. Second, the minimum prescribed thickness ensures that the pads will have the required abrasion and scuff resistance over a sufficiently long period of time. Typically, however, in order to reduce the cost of such pads, they are manufactured with heavy concentrations of filler materials such as calcium carbonate, a material which actually reduces the scuff and abrasion resistance of unfilled polyvinyl chloride.
It has now been found that many of the above problems relating to the prior art dielectric process and the deficiencies of the hot melt adhesive applications can be solved by the process and products according to the present invention. In particular, it has now been found that an adhesive may be applied to the total area of an unpatterned blank (as opposed to a pre-molded and pre-patterned) PVC heel pad to automotive carpeting to simultaneously form a design configuration or pattern on the blank pad during a single bonding and molding operation. Thus, the lamination process according to the invention entirely eliminates the need for pre-molded (pre-patterned) heel pads.
The process according to the present invention includes the following basic steps:
(a) placing an unpatterned pre-cut PVC heel pad onto the face of a conventional pattern mold;
(b) depositing a uniform layer of liquid hot melt adhesive to the exposed surface of the unpatterned flat heel pad (preferably in an amount equal to approximately 8 ounces per square yard), with the liquid hot melt adhesive being formable into a coherent solid layer upon fusion and solidification during cooling;
(c) immediately contacting the tufted or fibrous surface portion of an automotive carpet to the hot melt adhesive; and
(d) applying uniform pressure to the mold, unpatterned heel pad and automotive carpeting to adhesively bond the heel pad to the carpet and simultaneously form, in situ, a patterned heel pad.
Surprisingly and unexpectedly, the method according to the present invention has a number of distinct advantages over conventional pattern molding operations. First, as discussed above, the simultaneous molding and adhesion of the PVC pad during the hot melt application eliminates the need for utilizing pre-formed heel pads, i.e., pads having design patterns already imprinted on the exterior surface. Second, it has been found that the use of hot melt adhesives in prescribed amount and within certain temperature ranges permits the design to form on PVC heel pad blanks having thicknesses well below conventional 40 millimeter pads during the single lamination step. For example, PVC thicknesses as low a 7 millimeters have been found to be acceptable. Despite the reduced thickness of heel pads in accordance with the invention, they have been found to exhibit improved wear and scuff resistance (due primarily to the absence of high concentrations of filler materials used in conventional heel pads, e.g., up to 30% by weight).
It has also been found that the method and products according to the present invention may be used with an entirely new and unexpected category of carpets. It is well known in the automotive carpet industry that nylon face fiber carpets will bond effectively to PVC materials such as heel pads using conventional dielectric means. However, polypropylene face fiber products will not bond effectively to PVC pads using dielectric means without special costly pretreatments or costly modifications to the process because of the absence of polar groups in the polypropylene fibers. Thus, to date, almost 100% of the carpet face fibers used in molded automotive floor coverings are composed of Nylon 66 or polymerized polyhexamethylene adipimide using dielectric means to bond the heel pad to the carpet. The current industry trend is to improve ultra violet light fastness while reducing the cost of fibers. As a result, recent efforts within the industry have focused on replacing BCF nylon with polypropylene because the latter is capable of solution (pigment) dyeing which produces superior light fastness to conventionally dyed nylon. Polypropylene is also lower in cost than nylon.
Surprisingly, the hot melt adhesive method in accordance with the present invention is effective in simultaneously pattern forming and bonding PVC heel pads to polypropylene. Thus, the present method offers an improved design/bonding lamination method for polypropylene carpets which cannot be readily duplicated by currently available dielectric processes.
Although the exact mechanism for forming a design on the PVC blank pad is not known, applicants believe that when the hot melt adhesive comes in contact with the surface to be bonded--in this case the coated side of the PVC vinyl sheet--a high degree of wetting of the hot melt coating and the surface material occurs as the two components (PVC and adhesive) make contact. The adhesive immediately transfers heat to the PVC under the coating and, to a limited extent, to the processing environment on the other side of the coating until an equilibrium temperature is attained. Within seconds, however, the high temperature differential driving force causes the thin PVC to reach a high enough temperature to undergo permanent deformation. In that regard, Table I is exemplary of the relationship of temperature and elapsed time after applying the hot melt adhesive to the PVC in accordance with the invention.
TABLE I ______________________________________ RELATIONSHIP OF PVC TEMPERATURE VS. ELAPSED TIME TIME TEMP. NO. 2 (.degree.F.) (SEC.) TEMP. NO. 1 (.degree.F.) (RECHECK) ______________________________________ 5.sup.1 366 364 10 358 360 15 342 351 20 327 344 25 316 333 30 305 311 35 294 289 40 283 287 45 271 268 50 261 258 55 250 243 ______________________________________ Notes: .sup.1 The hot melt adhesive was sprayed onto the PVC for 5 seconds. The first and second (recheck) temperature readings of the PVC were then take immediately thereafter.
As the mold is closed and pressure applied to the PCV/adhesive/carpet combination, the mold design configuration is permanently embossed on the PVC sheet. Typically, the total elapsed time from application of the adhesive to full compression and molding falls in the range of between 10-15 seconds.
Another advantage of the process according to the present invention is that it offers significant cost savings over prior art methods for adhering PVC pads to automotive carpets which require dielectric means.
The present simultaneous adhesive/design molding lamination technique also utilizes a significantly thinner PVC blank (generally in the range of 12 millimeters or less) and forms, in situ, a composite structure wherein the thin PVC forms a protective cover adhesively bonded to a layer of compressed fiber tufts in the carpet which have become saturated (impregnated) with the liquid hot melt adhesive. Upon cooling and compression, the adhesive-soaked fibers form the same design configuration as the vinyl covering and the pattern mold used during the process, thus completing a matrix or composite superior in performance and appearance but with substantially lower raw material and operating costs.
In its final state, the resultant pad defines a unitary, composite structure with the PVC surface having improved scuff and abrasion resistance as compared to conventional pads with thicknesses in the range of 30-50 millimeters. One reason for such improved wear characteristics is the fact that the thinner PVC blanks do not require any high concentration of fillers, such as calcium carbonate, which tend to reduce the abrasion and scuff resistance of conventional heel pads.
One further advantage of the present invention is that the heel pad location may be more accurately controlled than with conventional dielectric processes. Typically, dielectric methods of applying heel pads to unmolded carpets must allow for about one-fourth to one-half inch variation in pad location, with the best results being about 5-6 mm tolerance on flat carpet. In contrast, hot melt laminations in accordance with the present invention allow the heel pads to be applied to pre-molded (as opposed to flat) carpet and thus provide control within tolerance of about 3-4 mm. Such improved quality assurance applies both to heel pads affixed to the flooring area of the automotive carpet and those located partially on contoured sections such as, for example, up the transmission tunnel.
Thus, it is an object of the present invention to provide for an improved and more cost effective method for applying a PVC heel pad to automotive carpeting without requiring dielectric means.
It is a further object of the present invention to provide a novel heel pad which has improved wear characteristics and which eliminates unsightly "scuff" marks which occur with the use of conventional heel pads requiring high concentrations of filler materials.
It is still a further object of the present invention to provide for a simultaneous adhesive/design molding lamination method wherein polyvinyl chloride heel pads may be bonded to polypropylene carpet.
It is still a further object of the present invention to eliminate the necessity of pre-forming a heel pad applied to carpeting during the hot melt lamination.
It is still a further object of the present invention to provide an improved laminated carpet product having a heel pad adhesively applied in accordance with the invention.
It is still a fur&her object of the present invention to form an in situ pattern molding on the PVC pad simultaneously with the adhesion of the hot melt adhesive to the carpet and back side of the PVC sheet.
These and other objects of the invention will become more clear following consideration of the detailed description and appended drawings.